Atopic dermatitis (AD) refers to an inflammatory skin lesion caused mainly by an external stimulus, and is accompanied by chronic repetitive intense itching. The mechanism of AD development is poorly understood. However, it is understood that AD development has a genetic background. The serum of an AD patient contains a high level of IgE. Further, activated T cells, basophils, and mast cells are deeply involved in the mechanism of AD development. Particularly, these cells are activated when IgE. molecules binding to Fcε receptors (FcεR) on the mast cells or the basophils are cross-linked by allergens. As a result, Th2 cytokines (i.e., cytokines derived from type 2 helper T (Th2) cells) and chemical mediators (derived from the Th2 cells) are produced. It is supposed that this causes AD development. Important examples of the Th2 cytokines are IL-4, IL-5, IL-9, and IL-13. Important examples of the chemical mediators are histamine, serotonin, and leukotriene.
When helper T (Th) cells are antigenically stimulated, the Th cells produce the cytokines. Based on patterns in which the helper T cells produce the cytokines, the Th cells are categorized into two subgroups: Th1 cells and Th2 cells. When the type 1 helper T (Th1) cells are stimulated, the Th1 cells produce Th1 cytokines such as IFN-γ, IL-2, and TNF-β. When the type 2 helper T (Th2) cells are stimulated, the Th2 cells produce Th2 cytokines such as IL-4, IL-5, IL-10, and IL-13. The Th1 cells mainly induce cellular immunity, and the Th2 cells induce humoral immunity and sometimes induce an allergic response. When naive T cells are antigenically stimulated in the presence of IL-12, the naive T cells are differentiated into Th1 cells. When the naive T cells are antigenically stimulated in the presence of IL-4, the naive T cells are differentiated into Th2 cells.
IL-18, immediately after its discovery, drew attention as a factor inducing T cells and NK (natural killer) cells to produce IFN-γ (Okamura, H. et al. Nature 378, 88 (1995).). However, IL-18 must coexist with IL-12 before it can exert such a function (Nakanishi, K. et al., Annu. Rev. Immunol., 19, 423 (2001)). Further, INF-γ, which is a type of Th1 cytokine, blocks the action of IL-4, which is a type of Th2 cytokine. Therefore, it was supposed that IL-18, which induces IFN-γ, suppresses an immune response and exhibits an antiallergic action.
When a mouse is infected with a parasite, Th2 cells are induced and IgE is produced. The inventors has revealed that administering IL-12 and IL-18 to the mouse right after the infection induces IFN-γ production from the T cells, NK cells, and B cells and thereby suppresses IgE production (Yoshimoto, T. et al., Proc. Natl. Acad. Sci. USA., 94, 3948 (1997)).
Furthermore, the inventors have also revealed that administering only IL-18 increases IgE production (Yoshimoto, T. et al., Proc. Natl. Acad. Sci. USA., 96, 13962 (1999)). Further, a subsequent analysis has revealed that administering IL-18 to a healthy mouse induces IgE production (Yoshimoto, T. et al., Nat. Immunol., 1, 132 (2000)).
IL-18 administered into a living organism acts on CD4 positive T cells (CD4+ T cells) to induce expression of a CD40 ligand (CD40L) and production of IL-4, IL-5, IL-13, and the like (Yoshimoto, T. et al., J. Exp. Med., 197, 997 (2003)). Further, B cells produce IgE when the B cells are stimulated in vivo by CD40L and IL-4. The CD40L was expressed by the IL-18-stimulated CD4 positive T cells.
IL-18 in vitro acts on basophils and mast cells, both of which are induced by IL-3, to induce production of IL-4, IL-13, histamine, and the like (Konishi, H. et al., Proc. Natl. Acad. Sci. USA, 99, 11340 (2002)).
According to a conventionally accepted theory, as described in the beginning, it has been held that mast cells are activated when allergens bind to a plurality of IgE molecules binding through Fc sites to FcεR on the mast cells and thereby cross-link these IgE molecules. Although this accepted theory still hold true, the inventors have revealed that even in the absence of an allergen and IgE, IL-18 directly activates mast cells and basophils to induce production of IL-4, IL-13, histamine, and the like (Yoshimoto, T. et al., Proc. Natl. Acad. Sci. USA., 96, 13962 (1999)). Also in such a case, allergic inflammation occurs.
IL-18 is produced as a biologically inactive precursor (IL-18 precursor), activated when cleaved by caspase 1, and then secreted extracellularly (Gu, Y. et al., Science, 275, 206 (1997)). The inventors found that IL-18 precursors are produced and accumulated in cutaneous keratinocytes. Based on this finding, the inventors produced a mouse (caspase 1 transgenic mouse) in which caspase 1 is overexpressed specifically in cutaneous keratinocytes (Yamanaka, K. et al., J. Immunol., 165, 997 (2000)). As a result, in the mouse, a large amount of biologically active IL-18 was produced. Further, in the mouse blood, a large amount of IgE was produced (Yoshimoto, T. et al., Nat. Immunol,. 1, 132 (2000), Konishi, H. et al., Proc. Natl. Acad. Sci. USA, 99, 11340 (2002)). Furthermore, although the mouse was grown in an allergen-free environment, the mouse developed intense atopic dermatitis (Konishi, H. et al., Proc. Natl. Acad. Sci. USA, 99, 11340 (2002).
Incidentally, it has become clear that IL-4 and IL-13 exert their actions when their respective signals are transmitted through Stat6 into the nucleus of a targeted cell. The inventors have revealed that IgE is not produced in a Stat6-deficient mouse (Takeda, K. et al., Nature, 380, 627 (1996)). Moreover, the inventors mated the caspase 1 transgenic mouse with such a Stat6-gene-deficient mouse so as to produce a Stat6-gene-deficient caspase 1 transgenic mouse. As a result, the inventors found that the Stat6-gene-deficient caspase 1 transgenic mouse developed intense atopic dermatitis, even though the mouse produce no IgE (Konishi, H. et al., Proc. Natl. Acad. Sci. USA, 99, 11340 (2002)).
Meanwhile, the inventors mated the caspase 1 transgenic mouse with an IL-18-gene-deficient mouse so as to produce an IL-18-deficient caspase 1 transgenic mouse. It was found as a result that the IL-18-deficient caspase 1 transgenic mouse had a large amount of IgE in the blood, even though IgE production was suppressed. However, in the mouse, although IgE was produced, the development of atopic dermatitis was completely. suppressed (Konishi, H. et al., Proc. Natl. Acad. Sci. USA, 99, 11340 (2002)).
From these results, it can be said that atopic dermatitis can-be treated more effectively by inhibiting the action of IL-18 than by suppressing IgE production.
Immediately after its discovery, IL-18 was called an INF-γ inducing factor. As the name implies, IL-18 acts on the Th1 cells or NK cells synergically with IL-12 so as to strongly induce INF-γ production (Okamura, H. et al. Nature 378, 88 (1995)., Nakanishi, K. et al., Annu. Rev. Immnuol., 19, 423 (2001)). Furthermore, IL-18 enhances expression of a Fas ligand (FasL) on these cells (Tsutsui, H. et al., J. Immnuol., 159, 3961 (.1997)). When FasL is a trimer, FasL induces cell apoptosis.
The inventors have reported that Fas is expressed by Kupffer cells that exist in the liver of a mouse to which Propionibacterium acnes has been administered, and that FasL stimulates the Kupffer cells to produce active IL-18 (Tsutsui, H. et al., Immunity, 11, 359 (1999)). Furthermore, IL-18 acts on the NK cells and Th1 cells to enhance FasL expression. Thus, it has become clear that there is a positive correlation (positive feedback loop) between IL-18 and FasL (Tsutsui, H. et al., J. Immunol., 159, 3961 (1997), Tsutsui, H. et al., Immunity, 11, 359 (1999), Tsutsui, H. et al., Immunol. Rev., 174, 192 (2000)). Therefore, it has become clear that when IL-18 is overproduced in vivo, serious damage to the liver and intestine is caused. As these findings show, IL-18 also causes so-called Th1 diseases.
It has been suggested that IL-18 is also involved in Th1-cell-induced bronchial asthma and other diseases, as well as the diseases named above.
As described above, controlling production or activity of IL-18 plays an extremely important role in a method for treating IL-18-dependent disease or Th1 disease. A typical example of the IL-18 dependent disease is IL-18-dependent atopic dermatitis. The Th1. disease is a type of disease developed or exacerbated due to overproduction of IL-18.
Therefore, if a specific monoclonal antibody that neutralizes the physiological activity of IL-18 were developed, such a monoclonal antibody would serve as a means of effectively treating many types of IL-18-related diseases.
In reality, only a few mouse- and rat-derived monoclonal antibodies have been obtained as antibodies against human IL-18 (anti-human IL-18 antibodies) (For example, Japanese Unexamined Patent Publication No. 236884/2000 (Tokukai 2000-236884; published on Sep. 5, 2000), International Application No. WO00/56771 (published on Sep. 28, 2000).
However, the conventional anti-human IL-18 antibodies are mostly monoclonal antibodies derived from nonhuman animals, and when such antibodies are administered to a human, the antibodies are recognized as foreign substances and rejected as such. Therefore, it is difficult to use the conventional anti-human IL-18 antibodies as therapeutic drugs for human-IL-18-related diseases. Particularly, because the antibodies are administered continuously for a prolonged time period in order to treat autoimmune disease, this raises such a problem that antibodies are produced against the administered antibodies.
This problem may be solved by biogenetically humanizing the mouse anti-human -IL-18 monoclonal antibodies.
However, while humanization of the mouse monoclonal antibodies reduces antigenicity, there is a possibility that, when the humanized anti-human IL-18 antibodies are administered to a chronic autoimmune disease patient repeatedly or for a prolonged time period, antibodies (blocking antibodies) are produced which block activity of the humanized IL-18 antibodies. As a result, a remarkable therapeutic effect is not achieved. In some cases, there is a possibility that some serious side effects are produced.
Therefore, there is a strong demand for development of an anti-human IL-18 antibody that ensures a high level of safety even when administered repeatedly or for a prolonged time period.
The present invention has been made in view of the foregoing problems and has as an object to provide (i) a human anti-human interleukin-18 antibody which assures safety and a therapeutic effect and (ii) a fragment thereof, and to propose (iii) a method for using the antibody and fragment.